Mastery: Master Demonologist is a passive warlock ability learned at level 80 for those with the Demonology specialization. It increases the damage done by minions, and damage dealt while in caster or [demon] form.

Patch changes

Patch 4.3.0 (29-Nov-2011): Master Demonologist now grants a base bonus of 18.4% and 2.3% per mastery, up from 16% and 2% per mastery.